Surface discharge spark plug fob



June 2, 1953 w. B. SMITS 2,540,473

SURFACE DISCHARGE SPARK PLUG FOR LOW VOLTAGES AND CONDENSER DISCHARGE Filed April 14, 1951 lnvenior By ytz? Bokmm'li Attornuy Patented June 2, 1953 SURFACE DISCHARGE SPARK PLUG FOR LOW VOLTAGES AND CONDENSER DIS- CHARGE Wytze Beye Smits, Voorburg, Netherlands, assignor to Smitsvonk N. V., Rijswijk, Netherlands; a company of the Netherlands-" Application April 14, 1951, Serial N 0. 221,000 I l In the Netherlands April 19, 1950 1. The invention relates to a surface discharge spark plug for low voltages and condenser discharge, in which plug there arranged b8- tween the electrodes a separating body, over the surface of which the spark is formed, the distance between the active parts of the electrodes being less than or equalto 0.7 mm.

Spark plugs ofthis type are known, for example from Netherlands patent specification No. 46,114. In such plugs there is formed, over the surface of the separating .body, aflame spark which extends as it were in the shape of a flame over a certain area in' the gas mixture and is not merely confined to the surface in the manner of a creeping discharge. It is known that the separating body of such spark plugs is eroded, resulting in gradual wear or, with some insulating or semi conductive materials, to be used as the separating body in crumbling thereof.

, The chief object of the invention is, to minimize such erosion of the separating body and to prevent any crumbling of the material of which it is made.

To achieve this object, the invention; is mainly characterized by the separating body consisting of insulating or only slightly conductive material in which one or more metal reinforcing elements or layers are incorporated.

According to an additional feature of the invention, the reinforcing layers are approximately perpendicular tothe active surface of the separating body and extend down the separating body beyond the maximum active depth to which the separating body is eroded when in use.

The invention will now be explained more in detail with reference to an embodiment illustrated in the drawing.

Fig. 1 illustrates a spark plug according to the invention, partly in front view and partly in cross-section.

Fig. 2 illustrates another embodiment of a spark plug according to the invention.

Fig. 3 illustrates on a greatly enlarged scale a detail of the active area at the bottom of Figs. 1 and 2.

The spark plugs of Figs. 1 and 2 have a connecting terminal I an insulator body 2, and a casing 3 having a screw-threaded extension 4, which can be screwed into the metal body of the engine or the like in which the plugs are to be used, thus establishing contact with the said body (mass).

The active part of the spark plugs is illustrated in cross-section at the bottom of Figs. 1 and 2.

, I in contact with the spark plug.

6 Claims. (Cl. 123-169) This part has an inner electrode 5, which may be circular and which is conductively connected with the connecting terminal 5. In addition this part has an outerelectrode 6, which is annular, completely encloses the inner electrode 5, and is separated from the latter by a distance of 0.7 mm. or less. This outer electrode 6 is conductively connected with the body of the engine or the like through the screw-threaded part 4 of the plug casing 3. Between the electrodes 5 and 6 there has been disposed a separating. body l consisting of insulating or only slightly conductive material. In the spark plug according to Fig. 2 the active part extends a short distance into the engine, while the electrodes 5 and 6, and the separating body 1, are so designed that the flame spark is formed at a point of the cylindrical surface. I V

This spark plug operates as follows:

When a condenser discharge takes place in t e ignition system, there is formed, over the surface of the separating body 'lbetween the electrodes 5 and 6, a flame spark which initiates the ignition of the combustible gas mixture which is Fig. 3 illustrates how the separating body between the electrodes can be reinforced according to the invention. This figure again shows the part of the electrodes 5 and 6 in the active area at the bottom of Fig. 1., Between the electrodes, the separating body 7 is shown. The flame spark forms along the active surface 8. In this process the material of the said separating body is eroded, so that it crumbles or wears out, and the flame spark forms further and further down between the electrodes. Naturally the electrodes themselves are also slightly eroded. The spark plug here illustrated will be usable until the flame spark forms approximately along a line of dashes drawn in Fig. 3, which is desi nated by 9.

In the separating body I there have been shown a number of metal reinforcing elements H], II, and I2. These reinforcing elements are in the form of layers, and extend from theactive surface 8 in the separating body to some distance beyond the line 9. In the spark plugs here illustrated, in which the electrodes 5 and 6 are limited by circles, the metal elements are preferably of annular shape, so that they are at a uniform distance from each other and from the electrodes 5 and 6 throughout their circumference. These reinforcing elements [0, II, and 12 may consist of thin metal foil or of thin metal gauze. To the left of the reinforcing element H, the separating body is shown as consisting of an amorphous mass. This mass may first be built up together with the reinforcing elements Without anymutual cohesion, whereupon it may be firmly integrated by means of a heat treatment. To the right of the reinforcing element II the separating body is shown as consisting of layers, for example mica scales. The reinforcing element [2 forms the separation between the scales, which are parallel to the element H to the left of the said element 52, and parallel to the wall of the electrode 5 to the right of the element [2. These mica scales have a very considerable tendency to crumble near the active surface 8 when the spark plug is in use. This is effectively prevented by means of the reinforcing elements shown in the figure.

Instead of using metal foil, it would also be possible to provide metal layers against layers of the insulating material, for example, by sprayirig ordepositing from the vapor phase. On the other hand it is possible to -build up the separating body of layers of reinforcing material provided with insulating material on one or on both sides.

The proportion between the total thickness of the reinforcing material and that of the insulat ing material, measured along the active surface Belong the distance between the electrodes 5 and 6 is preferably less than 2. The reinforcing elements have no adverse eilfect on the formation of thefiame spark, and they constitute aneffective reinforcement, so that the separating body wears out less rapidly. If the above proportion between the total thickness of the reinforcing material and the total thickness of the insulating material is chosen, it is ensured that the reinforcing material will be eroded to practically the same extent as the insulating material, so that the active surface 8 will remain almost flat while proceedingtowards the line 8, thus ensuring eiiectiveoperation.

Themetals'preferably tobe used for the reinforcing elements are iron, copper, more precious metals, such as silver, or alloysof these metals.

It is cbvious'that the reinforcing elements. may be-conductivelyinterconnected. If such a con nectionis considered desirable, it. is to. be.- preterred to establish it inside the separating body Tbeyond the line 9.

What'I claim: is:

1. Low voltage discharge spark plug including at least. twov coaxially extended. electrodes, one

surrounding the other, both electrodes facing each other at their sparking end faces with circular rims, the rims projecting towards each other and leaving a narrow gap therebetween, substantially not wider than 0.7 mm, and a separating insulating body of at most slight conductivity disposed between said electrodes and having a projection reaching through the gap with its end surface flush with said sparking end faces so as to constitute therewith the active surface of the spark plug; the depth of the gap being proportioned so as to determine the depth of erosion to be admitted through use of the spark plug; at least one thin metallic layer being inserted into the projection of said separating body and extended from the active surface through and beyond the depth of the gap, peripherally around the same and spaced apart from both rims, thereby to re-enforce the material of said projection, said layer being of a thinness to ensure its erosion under use of the spark plug to practically the extent of the erosion of the separating insulating material.

2. Spark plug as set forth in claim 1 wherein the metallic layer consists of metallic foil.

3. Spark plug as set forth in claim 1 wherein the metallic layer consists of metal gauze.

4. Spark plug as set forth in claim 1 wherein the separating body includes layers of insulating material extended within said projection in a direction along the depth of thegap and generally perpendicular to said active surface, at least one of the layers of insulating material having the metallic layer bonded thereto.

5. Spark plug as set forth in claim '1 wherein at least one of the sides'of said metallic-layer is faced with a layer of insulating material.

6. Spark plug as set forth in'claim 1 wherein, measured across the width-of the gap, the proportion of metallic layer to width-of the gap is less than one third.

WYTZE BEYE 'SMITS.

References Cited in the-file Of this patent UNITED STATES PATENTS Number Name Date 1,991,369 Berger Feb. 19,1935

FOREIGN PATENTS Number Country Date 536,460 Great Britain May-15, i941 

